In the manufacture of draw tape and draw string plastifilm bags, a tunnel structure containing the draw string(s) or draw strip(s) is provided around the mouth of the bag by hemming or turning edge portions of two panels forming the bag. A number of methods and apparatus have been employed in the past to provide these hems. Two examples of the prior methods and apparatus are provided by U.S. Pat. Nos. 2,897,729 to Ashton et al and 3,058,402 to Kugler. In Ashton, two superposed panels of a medianly folded plastifilm sheet are each outwardly hemmed by devices not depicted or described. While outward hemming of a pair of superposed panels is rapidly and easily accomplished, it provides an exposed hem on the outside of the bag which is not aesthetically pleasing. Kugler depicts the previously employed method of forming an inwardly hemmed bag: laying down draw tapes or draw strings on the same side of a flat, plastifilm sheet near the longitudinal side edges of the sheet; turning those longitudinal edges over the strips or strings and towards one another, and medianly folding the sheet once again in the same direction to place the inwardly turned edge portions between the panel portions. The drawback to this method is that the full width of a flat plastic sheet must be used in the early portion of the manufacture. Since the plastifilms involved are typically blown tube extruded, extra manufacturing steps are required to provide a fully flattened, single layer sheet. Moreover, considerable floor space is required in the manufacturing areas to provide sufficient room to work with the fully opened sheet.
A number of other patents describe or refer to the forming of one or more folds in thermoplastic film while forming plastic bag bodies or wrappers. U.S. Pat. No. 4,430,845 depicts a folder for polyfilms, utilizing large and small folding triangles on opposite sides of a folding board to turn in, first one and then the other free longitudinal edge of a flat, continuous, polyfilm sheet during the packaging of articles. U.S. Pat. Nos. 3,656,415, 3,954,049 and 4,138,932 depict and/or describe turning over one or both free edges of a flat, continuous, polyfilm sheet during the formation of bag bodies. None of these devices is suitable for providing a pair of inwardly turned hems in superposed plastifilm panels.
Another U.S. Pat. No. 3,720,141 relating to the manufacture of plastic carrier bags includes a "lip folding 5 apparatus 30" formed by sets of creasing rolls 32a-32d and related devices neither depicted nor described. The apparatus is described as being capable of turning adjoining, free longitudinal edges of the superposed panels of a medianly folded thermoplastic film inward once or twice, if desired, to form a pair of hems along one longitudinal edge of the film. The use of moving parts needed for this apparatus adds to its cost of manufacture and the number of rollers involved (at least four) and required other devices add further to the cost of manufacture and take up more than an insignificant area in the manufacturing line.